The invention relates to a turning machine of the type which converts round bars of hot rolled steel to so called bright steel by means of turning. This rod shaped round material is turned at its cylindrically shaped periphery by means of a rotating cutter-head. The rod itself is secured against undesired rotation and is guided axially through the central bore of the cutter-head of the turning machine. The rotating cutter-head supports three or more inwardly directed cutters which cut the surface of the rod along a helically shaped path. Such turning machines are conventionally used with wires, rods and pipes. The state of the art turning machines show advancing means including an infeed device with advancing rollers which are disposed on the inlet side of the cutter-head. Such an infeed device generally consists of two pairs of advancing rollers. The known bar turners of this type further comprise withdrawal means, e.g. a clamping carriage which is mounted on the outlet side of the cutter-head. The clamping carriage secures the rod against rotation and advances it, when the rear end of the rod is being turned.
Modern bar-turning-machines can be controlled as to their speed of advance, the speed of the cutter-head and the turned diameter of the bars during the operation of the machine.
The basic construction of the turning machine of this invention jointly with an infeed-device is disclosed in German Published application No. DE-A1 33 46 613. In this known arrangement the rod is guided by a so called "rear guide" at the outlet side, downstream of the cutter-head, within the hollow shaft. A guide arrangement for rods in turning machines of the aforedescribed type is described in German Published application DE-A1 32 40 146 and the corresponding U.S. Pat. No. 4,634,323. The construction and rigid connection between the tensioning arm, guide element and pivot shaft is illustrated in FIG. 2 of German Published Application No. DE-A1 33 46 613. The rear guide is mounted on the machine frame and extends into the rotating hollow shaft up to the region of the cutter-head. This known rear guide mechanism has individual spring biased guide elements, which abut against the work piece and has a central adjustment mechanism for all guide elements. The central adjustment mechanism is also spring biased. A drawback of such a turning machine having a rear guide mechanism is that the centering effect for guiding the turned rods is insufficient for maintaining the rod at the machine center. It is an object of the present invention to provide a turning machine having a rear guide mechanism in which the centering effect and the individual spring biased support effect are combinable in any predetermined fashion in accordance with the requirements of individual operational conditions.
This object of the invention is achieved by providing a turning machine with two stops for each one of the individual guide elements in a guide mechanism in the proximity of the cutter head, one of which stops is rigid and the other one is resilient. The rigid stops delimit the deflection of the resilient stops for the individual guide elements. "Rigid" refers to the individual movement of the guide elements relative to the central adjusting mechanism.
Preferably the forces of the spring means for the individual guide elements are adjusted in such a way that the sum of their forces is inferior to that of the central adjustment means.
A further embodiment of the invention includes the possibility of preselecting the individual spring rates or forces of the guide elements. A tighter individual spring support can be adjusted as well as of course a tighter central spring support.
In a preferred embodiment of the invention the guide elements are adjusted in such a way that their resilient stops do not define their position in normal operation. The springs for biasing the individual guide elements are deflected so that the individual guide elements, i.e. their tensioning arms abut against the rigid stops. Initially only the spring biased central adjustment mechanism by means of which all of the guide elements are synchronically and centrally opened, respectively closed, is effective. This serves the purpose of absorbing the tolerances of the diameter of the turned rod and a reliable contact of all guide elements with the rod and a concentric position with the machine center.
The particular advantages of the construction of the invention become obvious when a stiff and slightly curved rod which cannot be forced by means of the guide mechanism exactly into the center of the machine, is nevertheless sufficiently guided by the inventive arrangement. In such a case the curved rod presses the guide element, hindering it from taking an operative position so strongly, that the central adjustment mechanism of the guide elements opens the caliber of the arrangement. Nevertheless, the turned bar in the range of the rear guiding system cannot oscillate within the enlarged caliber. This is prevented by the springs of the remaining guide elements which cause these guide elements to follow the rod, when it leaves the center of the bar turner. These remaining guide elements abut only against the peeled and curved rod by virtue of the force of their individual springs.
This solution combines the advantages of a prevailing centering effect and a complementary individual resilient support of the bar by a set of guide elements during the turning process.
In order to achieve an adjustment of the rear guide mechanism for individual operative requirements a further embodiment of the invention includes means to adjust the force of the springs of the individual guide elements as well as the force of the central spring support.
The inventive arrangement provides first of all a very strong centering effect with the spring means for the individual guide elements being supressed. For this purpose the turning machine is adjusted and operated so that the individual spring supports will, mainly in the rare instance, when a very stiff and curved rod must be turned, complimentarily and auxiliarily support the deflected central spring support. In normal operation the individual guide elements are backed up only by the rigid stops.
The aforedescribed features for the rear guide mechanism may be transferred to a forward guide mechanism as well which is mounted between the infeed mechanism and the cutter-head.